Presently available selective catalytic reduction (“SCR”) systems adsorb ammonia (NH3) on a catalyst and then react the NH3 with NOx to reduce the NOx emissions. The NH3 is typically stored as a less reactive composition, e.g. urea, and hydrolyzed into NH3 in the exhaust system as required to reduce the NOx emitted by the engine. At certain system operating conditions, the NH3-based NOx reduction mechanism breaks down due to lack of NH3 storage capacity on the SCR catalyst, due to an inability to rapidly hydrolyze urea into NH3, or for other reasons. Various factors limit low temperature performance of aftertreatment systems due to the evaporation, thermolysis and hydrolysis of the urea solution and the kinetics of the chemical processes, even in the presence of a catalyst. When the NH3-based NOx reduction mechanism breaks down, the net NOx emissions of the system increase.
Current techniques for management of aftertreatment system temperature involve warm-up strategies to rapidly increase the SCR catalyst from a cold start condition to a temperature effective to hydrolyze urea to manage NOx emissions. Certain operating conditions after warm-up of the SCR catalyst cause the catalyst temperature to drop below an optimal or desired temperature for effective hydrolysis of urea. Current techniques to maintain SCR catalyst temperature above a minimum threshold include, for example, controlling actuators in the air handling systems and adjusting the combustion processes in the cylinders to increase exhaust gas temperature. However, these techniques can be inefficient, and can further increase engine output of particulates, requiring the aftertreatment system to include a particulate filter. In addition, therefore, improvements in this technology are needed.